1. Field
Disclosed herein is a magnet core pressed using an alloy powder and a pressing additive to form a composite. Also disclosed is a method for producing a magnet core of this type.
2. Description of Related Art
The use of powder cores made from iron or alloy powder has been established for many years. Amorphous or nanocrystalline alloys, too, are increasingly used, being superior to other crystalline powders, for example in their remagnetisation properties. Compared to amorphous powders, nanocrystalline powders offer the advantage of higher thermal stability, making magnet cores made from nanocrystalline powders suitable for high operating temperatures.
The raw material for nanocrystalline powder cores typically is an amorphous strip or a strip material made nanocrystalline by heat treatment. The strip, which is usually cast in a rapid solidification process, first has to be mechanically pulverised, for example in a grinding process. It is then pressed together with an additive in a hot or cold pressing process to form composite cores. The finished pressings may then be subjected to heat treatment for turning the amorphous material into nanocrystalline material.
EP 0 302 355 B1 discloses a variety of methods for the production of nanocrystalline powders from iron-based alloys. The amorphous strip is pulverised in vibratory or ball mills.
U.S. Pat. No. 6,827,557 discloses a method for the production of amorphous or nanocrystalline powders in an atomising process. This method involves the problem that the cooling rate of the melt depends heavily on particle size and that the cooling rates required for a homogenous amorphous microstructure are often not obtainable, in particular with larger particles. This results in powder particles with a strongly varying degree of crystallisation.
The level of iron losses is an important characteristic of magnet cores. Two factors contribute to iron losses, these being frequency-dependent eddy-current losses and hysteresis losses. In applications such as storage chokes or filter chokes, for instance, iron losses at a frequency of 100 kHz and a modulation of 0.1 T are relevant. In this typical range, iron losses are dominated by hysteresis losses.